The well-established aqueous or solventborne coating materials, particularly those known as basecoat materials, and the multicoat effect paint systems produced using them exhibit performance properties that are substantially good.
The continually growing technical, and more particularly esthetic, requirements of the market, particularly of the automakers and their customers, however, are necessitating a continual onward development of the technical and esthetic level attained to date. Modern bodywork design, with its pronounced rounding, fits in very well with finishes exhibiting a pronounced flip-flop effect. The desire to produce an effect resembling metal can be realized through the use of very thin aluminum flakes, with sizes in the nanometer range, of the kind described in EP 0826745 A2, for example.
More particularly, there is a need for new coating materials which allow production of basecoats exhibiting a particularly strongly pronounced light/dark behavior. At the same time, however, the advantages achieved by the known basecoat materials and the basecoats produced from them should not be lost, but should instead be retained to at least the same extent and preferably a greater extent.
The corresponding effect-imparting and also, where appropriate, color-imparting basecoats are therefore to possess, in particular, good haze behavior, i.e., no haze, good leveling, and a very good overall visual appearance. Furthermore, the basecoats are to be free from paint defects, light/dark shading (clouds), and bits. The resulting coatings are, furthermore, to have no optical defects and to possess satisfactory adhesion to the clearcoat.
The coating materials are additionally to feature high storage stability, i.e., no significant deterioration in the properties either of the coating materials or of the coatings produced from these coating materials after storage of the latter at 40° C. (for 28 days). Hence there is to be no significant deterioration in the rheological properties of the coating materials, more particularly no significant increase in viscosity, and no bittiness and no significant deterioration in metallic flop.
Conventional, prior-art aqueous basecoats are easy to produce, stable on storage and transportable. In terms of application, technological properties (adhesion, long-term weathering), storage stability and circuit line stability, and also in terms of appearance, they meet the requirements that are usual within automobile finishing.
EP 1 591 492 A1 describes, for example, a basecoat material which comprises metallic pigments, which can be aqueous or solvent-based, and which includes a relatively high fraction of the metallic pigment—preferably 12% to 20% by weight based on the total binder content. The focus of EP 1 591 492 A1, however, is on providing highly moisture-stable systems.
WO 2006/017197 A1 discloses a process for producing special-effect finishes, which uses relatively low fractions of a laminar metallic pigment with comparatively high quantities of binder and solids fractions in order to produce an effect paint, the paint requiring use not only of the laminar metallic pigment but also of at least one further, additional special-effect pigment.